Question

X-linked recessive disorders are passed from mothers to their sons and from fathers to their daughters. If a male expresses a X-linked recessive disorder, then which of the following is true for his parents?
I. His mother is a carrier.
II. His father expresses the same disorder.
III. His mother does not express the disorder.

• A. I only
• B. II only
• C. I and II only
• D. II and III only
• E. I, II, and III

Answer 1

The correct option is A I only

The statement I is correct as carrier mother will pass affected X chromosome to 50% sons and normal X chromosome to rest 50%. Hence, the male could have received the disease from the carrier mother. Statement II is incorrect as the diseased state of father does not determine the diseased state of the son. Statement III may or may not be correct as carrier mother would not express the disease but the colour blind mother would.

Therefore, the correct answer is option A.